As is well-known, thermostats control heating, ventilation, and air conditioning (“HVAC”) systems in buildings. A non-programmable thermostat allows a user, such as an occupant or building manager, to set one setpoint temperature for the heating season and one setpoint temperature for the cooling season to control the HVAC system. When the measured indoor temperature is below or above these setpoint temperatures, the HVAC system is activated. A programmable thermostat allows a user to program setpoint temperatures for different times of the day. For example, in the heating season, many users still set the thermostat to a lower set-back temperature at night. This temperature set-back reduces the amount of time that the HVAC system is activated in order to maintain the lower temperature and thus saves energy and money. However, the energy savings from such time-based programmed setpoint temperatures as compared to the comfort temperature that is set during the day is unknown to a user.
The Energy Star programmable thermostat specification has been in effect since April of 1995. The Energy Star specification states that a programmable thermostat is “a device that enables the user to set one or more time periods each day when a comfort setpoint temperature is maintained and one or more time periods each day when an energy-saving setpoint temperature is maintained.” The current specification defines comfort setpoint temperature as “the temperature setting in degrees Fahrenheit or degrees Celsius for the time period during which the building is expected to be occupied, e.g., the early morning and evening hours. The specification defines energy-saving setpoint temperature as “the setpoint temperature for the energy-saving periods usually specified for both the heating and cooling seasons. In the energy-saving mode, the thermostat setpoint may vary from the comfort setpoint temperature to the set-back temperature or the set-up temperature depending on the season. The set-back temperature is the setpoint temperature used during the heating season, normally at night or during unoccupied times of the day. This is a lower setpoint temperature than the comfort setpoint temperature. Similarly, the set-up temperature is a setpoint temperature used during the cooling season, normally at night or during unoccupied times of the day. This is a higher setpoint temperature than the comfort setpoint temperature. This specification has been confusing to users as to how to achieve energy savings from programmable thermostats. The EPA is considering issuing a new Energy Star specification in 2010. Even if the new specification is not finalized, the old Energy Star specification will be suspended due to the confusion to users.
Presently, users that invest in programmable thermostats to save energy and money do not have any ready means to determine how much energy and money is being truly saved. The programmable thermostats therefore are arbitrarily set at different temperatures, which may or may not save the user money and energy. Therefore, the present known programmable thermostats do not provide energy savings feedback to allow a user to adjust temperature setpoints and times based on how the building environment responds to changes in the internal and external environments.